Thermostatic element



July l, 1930. W, M, @HACE 1,769,623

' THERMOSTATIC ELEMENT Filed Aug. 1e, 1928 Joa zoo

A TTORNE Y.

Patented July l, 1930 UNITED STATES PATENT OFFICE WILLIAM M. CHACE, OF DETROIT, MICHIGAN; ADELBERT H. LINDLEY, ABTHIIB COOPER, .AND HILMA IB. CHACE, EXECUTORS 0F SAID WILLIAM M. CHACE, DE-v CEASED, ASSIGNORS TO W. M. CHACE VALVE COMPANY, OF DETROIT, MICHIGAN, L

CORPORATION OF MICHIGAN THERMOSTATIC ELEMENT Application mea August v1e, 192s. serial No. 299,957.

This invention relates to bimetallic elements consisting of two metal strips of dissimilar thermal characteristics and ordinarily used in the control of operation of various instrumentalities, and the purpose of the invention is to provide a bimetallic element capable of being subjected to fairly high heat without permanent deformation.

A further object of the invention is to provide a bimetallic element in which the dissimilar characteristics arey not materially apparent below 350 degrees F., or about 550 degrees F within which temperature range the dissimilar thermal characteristics are most pronounced.-

A bimetallic element of such specic character having such a short range ofdil'erence' in degree of expansion per degree of temperature change is very rapid in its action within the said temperature range and if for instance used in the making .or lbreaking of an electric circuit permits a ready adjustment of parts to insure the making or breaking of the-circuit, or other function depending upon the apparatus controlled, at a predetermined temperature.

A further feature of the invention is in the composition of elements permitting the same to be rolled in the usual manner while hot wit-hout the production vof scalev and subsequently finished to the desiredthinness while cold. Thus, in view of the absence of pitted surface, Very smooth polished surface is pro-v duced and a subsequent operation such as grinding or polishing is avoided'.

In attaining of these various objects I form the bimetallic element of two metals of dissimilar thermal characteristics both of which contain nickel. While it is well known to utilize nickell in both elements of a thermostatic couple, it has been usual to utilize a fairly high percentage'of copper in the expansion side but I have discovered a composition for the lexpansion side in which the nickel and copper content is small and having a coeilicient of expansion approximately equal to that of brass. This invention is more particularly directed toa composition of metals for'the expansion side in the provision of a bimetallic element having the characteristics stated. Preferably, however, what may be termed the neutral or nonexpansive side is formed of the following For the expansion side I use the followmg composition of elements substantially within the range of percentages statednamely,

Carbon .25 to .35

Silicon 1.75 to 2.00 Chromium 13.25 to 14.00 Nickel 7 .25 to 7.75 Copper 2.00 to 4.00 Wrought iron 72.50 to 71.90

The elements stated are the usualv commercial form and the iron utilized in the expanslon side is preferably what is knownas Sweedish iron particularly in view of its containing a trace of copper and therefore more readily combined with the copper.

In combining these elements I have discovered a method (which is the subject matter of another application for Letters Patent of the United States) whereby the copper is readily mixed with the iron with which it does not readily assimilate. This method consists in the combining of the copper and the nickel between which there is an aflinity and then combining the nickel-copper combination with the iron and other ingredients which is readily accomplished due to the aflinity between the nickel and iron.

A bimetallic element formed of the two composite metals welded together has the characteristic of temperature change as shown in the accompanylng diagram in which the horizontal lines indicating the temperalture and the heavy line with the curve showing the deformation of the thermostatic couple under temperature change. From this diagram it will be observed that at temperateristics are vnot pronounced, but from 350 to 500 degrees F., the movementis rapid. That is within this temperature range the dissimilar thermal characteristicsv are very pronounced and, at temperatures'above 550 degrees F., either the expansion is similar or the lmetals have practically reached `their limit l of expansion.

i tween the contactin rolled cold to the final thinness thereby producing a practically smooth finished surfaceas it comes from the rolls.v Consequently a final polishing operation is avoided.

,l One ofthe pur oses of the invention is Ato provide a bimeta lic element that has little movement outside a specific temperature range of about 200 degrees F., as is indicated bythe movement curve of the diagram. This diagram is platted from the behavior of a strip of metal .048 inch thick by one-half inch wide and 51/2 inches long held stationary at one end free to move at the opposite end.

It will thus be seen that I have secured a bimetallic element in which the greatest difference in degree of expansion per degree of temperature change is within a range of approximately 200 degrees F., and in which the Y movement 1s very rapid. This is of value in that it enables the structure with which my improved bimetallic element is to be utilized to be readily set to operate at a specific temperature within the said temperature range.

In bimetallic elements in which the dissimilar thermal characteristics are practically constant up to a point where permanent deformation takes place, it is a very diflicult matter to provide mechanical structures that would operate at predetermined temperature as the movement of the element is not restricted to any specific temperature range and an ideal bimetallic element for operation at a specic temperature would be one in which the movement was confined to just that temperature. This, of course, is impossible so far as I now know but I believe that in the provision of such an element in which the pronounced movement is practically confined to a range of approximately 200 degrees F., is a closer approach to the ideal condition than has heretofore been attained.

I have also found that by use of the composition stated I have secured a bimetallic element that may be subjected to temperatures as high as 2000 degrees F., kwithout permanent deformation. I

Having thus bri'eily described my invention, what I claim and desire to secure by Letters Patent of the United States is- 1.. A bimetallic thermostat consisting of two metal parts welded together, one of said parts consisting of the following elements approximately of the stated percentageviz:

Carbon Silicon 2.00 Nickel 40.00 Iron 57.65

and the other part consisting of the following elements approximately of the percentage stated-viz:

Carbon .25 to .35 Silicon 1.75 to 2.00 Chromium 13.25 to 14.00 Nickel 7.25 to 7.75 Copper 2.00 to 4.00 Wrought iron 72.50 to 71.90

Carbon .25 to .35 Silicon 1.75 .to 2.00 Chromium 13.25 to 14.00 Nickel 7.25 to 7.75 Copper- 2.00 to 4.00 Wrought iron 72.50 to 71.90

3. A bimetallic thermostat comprising two metallic elements secured together and having marked diierence in coeiiicients of expansion within a temperature ran e of approximately 200 degrees F., the sa1d diii'erences in coefiicient of expansion producing apractically 'constant degree of movement per degree of change in temperature within the said range, both elements having a predominant iron content and the element of lower coeflicient of expansion having as high as forty per cent of nickel and the element of higher coeiiicient of nickel content of not more than eight per cent, and a chromium content of approximately fourteen per cent.

4. A heat responsive device comprising two members secured together throughout their length, one being a corrosion resistant expansion having a iron alloy of chromium containin from 10 to 15% of chromium and the ot er member being an alloy of iron and nickel havin a coeiiicient of expansion less than that o the first said member.

5. A thermostatic device comprising two members united together, each having diswagens similar thermal characteristics and each consisting of an alloy of iron in a Predominatf ing amount, one member contaimng approximately 36% of nickel and the other member 5 from 10 to 15% chromium.

6. A. thermostatic device comprising two members united together, one composed of invar and the other of a high resistance iron alloy containing approximately 13% of. 10 chromium' Y In testimony whereof, I slgn thls specification. 

